“…Nanostructures that break time-reversal symmetry are highly desirable building blocks for next-generation all-optical signal processing circuits, providing analogues to the electrical diodes and transistors that have enabled today's computer and information technology. Diverse configurations have been proposed in order to realize asymmetrical light propagation, including devices based on magneto-optic effects [1][2][3][4], indirect interband photonic transitions [5][6][7][8][9], optoacoustic effects [10], nonlinear gain or absorption [11,12], parametric processes [13] as well as thermal nonlinearities. [14][15][16] Although these approaches have their own advantages, on-chip integration is still difficult to achieve since the structures demonstrated so far suffer from high complexity, costly fabrication, high energy consumption, small bandwidth or large footprint.…”